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Abstract:

Over the past 30 years, the flower development has been one of the main model to study the genetic control of organogenesis in higher plants. The work on Arabidopsis thaliana has led to the proposal of the ABC model of flower development. This model states the interaction of three classes of the genes that encode transcription factors specifying the four types of organs in the flower, i.e, sepals, petals, stamens and carpels. While the activities of these master regulators have been extensively characterized in recent years, comparatively little is known about the functions of the target genes of these regulators.
One of the genes that is acting downstream of AGAMOUS (AG) ? the transcription factor that specifies the formation of a carpel, is KNUCKLES (KNU). It has been reported that KNU is directly activated by AG and is believed to be a repressor of WUSCHEL (WUS) activity in the meristematic cells. To fully understand functions of KNU in the stem cells, several transgenic lines were generated. I used approaches allowing for knockdown of KNU functions in different regions of stem cells. I showed, that KNU is expressed earlier in the flower development and interacts with the gene regulating the size of meristem.
Although, the functions that KNU plays in flower development were described over a decade ago, its additional roles have not been proposed. The genome-wide binding data of KNU and the gene expression changes upon perturbation of KNU functions are still missing. To address this knowledge gap, the main focus of this thesis was on the characterization of the role of KNUCKLES (KNU) on a genome-wide scale. Using genomic technologies, I showed that KNU directly regulates sets of genes that act in the meristem development and maintenance. I also presented evidence that KNU regulates key factors that suppress or activate the trichome formation. I further showed that KNU is involved in regulation of the hormone metabolism and balancing their levels.
In the second part of this thesis, the dynamic distribution of epigenetic marks during early stages of flower development was investigated. The epigenetics is often defined as changes that are not caused by the modification in the DNA but instead by the DNA methylation or post-translational modification of the histones. These changes
have a substantial role in the processes that are involved in the formation and development of a flower. To better understand the mechanisms underlying the successful flower development, I used genome-wide approaches allowing for identification of interactions between the flower master regulator APETALA1 (AP1) and the epigenome. For that, the specific gene regions that are repressed or activated by the selected methylation marks were analyzed at different stages of flower development that is triggered by AP1. This work yielded in preliminary characterization of the interplay between the transcriptional regulation and the epigenetic mechanisms during the flower formation.